Progress of the TEO experiment at FLASH

Transcription

1 Progress of the TEO experiment at VUV-FEL at DESY - Armin Azima S. Duesterer, J. Feldhaus, H. Schlarb, H. Redlin, B. Steffen, DESY Hamburg K. Sengstock, Uni Hamburg Adrian Cavalieri, David Fritz, David Reis, Michigan University Ann Arbor, Michigan

2 Motivation TEO: Timing by Electro Optical sampling correlation between an optical laser pulse and the electric field of an electron bunch based upon Pockel s effect Purpose: jitter measurement for pump probe experiments electron bunch analyzing

3 Timing of TEO experiment - principle VUV-FEL e - TiSa - Laser oscillator Laser puls FWHM Δt FWHM = 60fs Phase-looplocked to FEL master oscillator pump synchronization / probe pump / probe synchronization synchronization synchronization OPA Delay line Amplifier Δt 153m bulk single mode polarization maintaining glass fiber e - e - TEO with EO-crystal Undulator t Pump probe e - t γ Goal: t - t < 50fs RMS Experiment

4 TEO detection area - top view EO-crystal material Δx 2mm started with: ZnTe μm, wedged e - IR today, resolution optimized: GaP 180μm

5 TEO signal detection side view Laser pulse Laser probe earlier later relative to electron bunch Idea: map temporal information into space Rotation of polarization ~ E r, which is! ~ ρ(z), the longitudinal electron density EO crystal (ZnTe, 300µm) (new GaP,180µm) e - e - e - e - e - Electron bunch

6 TEO signal detection polarizing beam splitter time time; space laser v k p polarized ICCD camera integrated intensity(a(a.u.) -10ps ps time Arrival time and duration of bunch is encoded on profile of laser Temporal resolution of Pump-Probe Probe exp. is given by the precision of the jitter measurement, actually 90 fs RMS.

7 TEO signal examples minimal width measured: 220fs FWHM (95 fs RMS) temporal resolution of TEO Having a peak of 220fs FWHM and 170fs rise time one expects to determine d the temporal location of the peak approximately with at least 50fs FWHM ( 20fs( RMS) precision.

8 Pump-Probe experiment in gaseous phase TiSa Δt (Xe) ΔE opt (1.5eV) E TOF (36.5 ev) E ion (13.4 ev) E FEL (48.6eV) FEL TiSa Magnetic bottle Xe, He, Ne, Kr B FEL v B Eret TOF- Spectrometer

9 Time of flight spectrum at temporal pulse overlap Time of flight spectrum of one pump-probe event in Xenon at

10 Pump-probe delay scan measurement Delay scan measurement of a Two-Colour Pump-Probe experiment in gaseous phase to generate sidebands of the main photo-emission lines of the spinorbit split states 5p 1/2 and 5p 3/2 of Xenon. The sideband amplitude is proportional to the degree of pulse overlap. Each spectrum shows an average over 200 time-offlight spectra per delay stage position. courtesy: S.Duesterer published in P. Radcliffe, S. Düsterer, M. Meyer, Applied Physics Letters 90, (2007)

11 Pump-probe experiment with fixed delay stage Pulse number [#] Single shot measurement of the previous pumpprobe system, now with a fixed delay stage. The ToF spectra are plotted in rows, while the spectral amplitude is colour-encoded In this case the temporal scan is performed by the temporal jitter itself!!

12 Sideband amplitude at fixed delay time -TEO sorting time ZERO #5 #1 #2 Δt jitter #3 #4 #6 -Δt jitter = -Δt TEO Pulse number [#] time [fs] Temporal jitter determines degree of temporal overlap and sideband amplitude. With the information of the temporal jitter measured by TEO the temporal pump-probe signal trace can be reconstructed. Temporal resolution is only limited by the detection error of TEO.

13 ToF data sorted by pulse number ToF data sorted by TEO time

14 TEO benchmark Δt TEO = 2 ( Δtsorted ) ( Δtoptimal ) 2 = 204 fs FWHM (87 fs RMS)

15 Dispersion during pulse transport Transport of laser pulse in Tunnel TEO time 150m Temperature change and micro-phonics in fiber changes the optical path length through the fiber and delays/accelerates the pulse for each event. This path length change is an error source for the arrival time measurement of TEO and must be compensated.

16 Feedback signal measurement To TEO exp. 50% back reflected Compensator Feedback control Feedback signal ( 3pJ) SHG+Photomultiplier BBO Oscillator probe pulse (60fs FWHM) about 840 ns 90 pulses between feedback signal and probe laser pulse Piezo Scanner Scanner 50Hz

17 Possible reason of TEO uncertainty

18 Conclusion 1. TEO is able to measure (indirectly) the relative arrival time between the NIR laser pulse used in a Pump-Probe experiment with the XUV pulse of. Presently the detection error for the XUV pulse arrival time is approx. 90 fs RMS, which has been demonstrated in a pump-probe experiment. 2. From this one can conclude, that TEO is also able to detect the electron bunch arrival of with a precision of at least 90 fs RMS. 3. A possible error source, which limits the timing detection of TEO has been identified. The fibre length varies statistically with 10Hz 100Hz by about fs RMS.

19 Temporal jitter studies of during the first beam period after shutdown (Nov.,Dez. 2007) ,15:47-16:12, 13.7nm, Energy level: 15.0muJ ,00:36-00:47, 13.51nm, Energy level 0.3muJ ,17:22-17:33, 26.05nm, Energy level: 10.0muJ , 08:54-09:14, 25.89nm, Energy level: 6.0muJ ,17:42-17:58, 26.11nm, 26.0muJ During time ,17:42-17:58, period from to the machine SASE jitter 26.11nm, independently from Energy the set level: wavelength. 26.0muJ Reason unknown.

20 Micro Bunch correlations TEO-BAM

21 Correlation BAM-TEO, EOS-TEO blue: EOS red: TEO Nov TEO fibre stabilization off Okt TEO fibre stabilization on (every 30sec)

22 Outlook Still to do: Fast fiber stabilization system will be installed. TEO times shall be easier to achieve and online available. New responsible scientist for TEO Nikola Stojanovic, 4504 Acknowledgements: Photon diagnostic: Stefan Duesterer, Harald Redlin, Paul Radcliffe, Josef Feldhaus Accelerator group: FLA: Holger Schlarb, Bernd Steffen, Florian Loehl, Peter Schmueser MSC4: Vladimir Rybnikov, Boris Fominykh, Vitali Kocharyan, Olaf Hensler, Gerhard Grygiel

23 END